Duplicating whole game as different version and renaming it

I have created a Single Player Game and would like now to make also a multiplayer version of it…

is there a way to duplicate a single version so it will be completely independent from original …
renaming everything as well as scripts so they would not interfere with original game

In my case manually doing it just does not work, it is a huge project , I am getting way too many errors and problems … prefabs seem to still stay connected to originals, they still end up loading original old scripts …

after 3 days of renaming still not getting anywhere…

I cant believe that people do a multiplayer version from scratch , has to be a way to keep single version while duplicating it into another independent version

thanks in advance

Look into Version Control.

Here is a random tutorial I found on the subject, for Mac but apparently works on Windows too:

http://adamsingle.com/unitygitsourcetreebitbucketmactute/

But basically, look into any kind of version control. GIT, Subversion, etc. You can make a branch of your project and make changes and still have your original branch somewhere else.

Hope this helps!